Spot welding tool for resistance welding of workpieces

Abstract

The invention relates to a device for protecting an electrode during the resistance welding of workpieces, in particular sheet metal. Said device comprises a strip that is placed over the electrode and can be displaced in relation to the latter, a backing material of said strip having an electrically conductive coating. To improve the welding quality, the coating is applied to the opposite side of the strip from the electrode and consists of a material, whose hardness is less than that of the backing material of the strip. The soft, electrically conductive coating improves the transfer of current from the electrode to the workpiece, thus preventing weld spatter and improving the welding quality.

The invention claimed is: 
     
       1. A spot-welding tool for resistance welding of workpieces made of aluminum and having a brittle oxide layer, comprising:
 at least one welding tong; 
 an electrode disposed on said at least one welding tong; and 
 a strip ( 1 ) placed over the electrode ( 2 ), in a manner displaceable relative to the electrode, 
 a pressure element movably arranged on the electrode in a region of an electrode cap, said pressure element being adapted to lift the strip off of the electrode during or after opening of the welding tongs and said pressure element being displaced relative to the electrode via a force application means when the welding tong is opened; 
 wherein a carrier material ( 14 ) of the strip ( 1 ) is made of steel and is provided with an electrically conductive coating ( 15 ), 
 wherein said coating ( 15 ) is arranged on the strip side facing away from the electrode ( 2 ) and is comprised of tin, and 
 wherein said tool is structured such that during welding, pressure from said at least one welding tong breaks the oxide layer of said workpiece, and said coating is pressed into gaps of the oxide layer of the workpiece. 
 
     
     
       2. A spot-welding tool according to  claim 1 , wherein at least two superimposed strips ( 1 ,  1 ′) are provided, wherein the strip ( 1 ) that comes into contact with the workpiece has the coating ( 15 ), which is of a smaller height than the carrier material ( 14 ) of said strip, on its side facing the workpiece. 
     
     
       3. The spot welding tool according to  claim 1 , wherein the force application means is an elastomer spring.